As a chemical substance which regulates plant growth, so-called plant hormones are known. Generally, a plant hormone is a chemical substance which derives from a plant itself and regulates growth, differentiation, or the like, of a plant in trace amounts. In addition, a variety of chemical substances which do not derive from a plant per se but regulate plant growth are also known.
For example, 2-azahypoxanthine is a 2-aza-substituted hypoxanthine having a purine skeleton, which is known not only as a degradation product of dacarbazine (DTIC) which is an anticancer agent, but is also known to contribute to improvement of the germination ratio and shoot elongation in seeds of bentgrass and rice, as well as root elongation, mass increase and the like in lettuce (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2009-1558).
Meanwhile, from the standpoint of agricultural policy, it is important to facilitate the growth of staple food crops, such as cereal crops including rice and maize and tuber crops, to increase the yield per unit area. In order to increase the yield of staple food crops, improvements have been made in fertilizers having high nutritional value; however, the adverse effects associated with the use of such fertilizers in large amounts have also been viewed as problematic.
From such standpoints as well, various plant growth regulators have been used, and for example, as an agent for increasing the yield of potato, C12-C24 monohydric alcohols such as stearyl alcohol (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2006-45144), triazole-based compounds (for example, see Japanese Patent Application Laid-Open (JP-A) No. 9-71) and the like are known.
Further, it has also been attempted to increase the yield by breed improvement and a transgenic rice is also known into which the cyclin A gene and the like are introduced in order to attain an increase in the seed mass, number of filled seeds, number of seeds, seed size, harvest index and thousand-kernel weight, as well as modification of the seed composition (for example, see Japanese Unexamined Patent Application Publication (Translated PCT Patent Application) No. 2007-515167 and Japanese Patent No. 4462566).